Target recognition by microRNAs

Recently, I broached the subject of small RNAs, and mentioned that there were two general classes of these regulatory RNA – microRNAs (miRNAs) and short interfering RNAs (siRNAs). These two classes of small RNAs recognize their targets by standard (Watson-Crick) base pairing. However, there are interesting differences regarding target recognition. siRNAs form duplexes that extend the length of the siRNA; this is not unexpected, as the siRNA is derived from a perfectly base-paired precursor that is usually derived from the target itself. miRNAs are a rather different beast; this is the subject of this essay.